In the field of diaphragm pump design, one of the most persistent problems in developing a lasting and efficient pump is in choosing a design which will eliminate or minimize diaphragm membrane rupture. It has not been uncommon to replace diaphragm membranes after only several hundred hours of use because of rupture and/or wear of the membrane, particularly when the pump is adapted for delivering higher fluid pressures. Diaphragm pumps may deliver 100-1,000 p.s.i. fluid pressures by moving the diaphragm membrane under hydraulic fluid pressure control, and so long as the pressure of the hydraulic driving fluid is equalized by the driven fluid pressure across the surface of the diaphragm the membrane will not rupture. However, transient pressure changes caused by intermittent delivery of pumped fluid, and by changes in the direction of diaphragm reciprocation, frequently cause pressure shock waves over portions of the membrane surface. These shock waves create extremely high instantaneous forces against the membrane and over a period of time may cause wear which eventually ruptures the membrane. It is desirable to minimize such shock waves, because the membrane, although inherently resilient, cannot indefinitely withstand large transient forces which are not distributed evenly over its surface.
Prior art devices have largely solved this problem by constructing surfaces in the diaphragm pumping chamber which limit the reciprocation travel of the diaphragm, but which have passages therethrough for the flow of pressurized hydraulic fluid. Under highly pressurized conditions these passages are subjected to transient hydraulic fluid pressures which are transferred to the adjacent membrane surface. For example, if the diaphragm membrane is reciprocated by means of a mechanically reciprocating piston acting upon hydraulic fluid, the change in reciprocation direction of the piston caused by a hydraulic shock wave to be propagated through the passages directly to the diaphragm membrane which is exposed by the passages. This causes an instantaneous force against that portion of the diaphragm membrane which does not become equalized until the membrane moves away from contact with the stop surface. Over a period of time this causes wear to the diaphragm membrane in the region adjacent the hydraulic fluid passages and ultimately will cause the diaphragm to rupture.